Cross a pretend stream in a race that requires both skill and speed.
Each player gets two stepping stones: old T-shirts, hand towels, or dish towels. At "Go," each player races to the finish line by standing on one stone, placing the second ahead of him, then jumping to that stone, without touching the grass. He then reaches back to retrieve the first stone, places it farther ahead, and so on.
Tossing the stone a long way may seem like the best way to move quickly, but if it's too far away, you'll have to leap to reach it -- and struggle to grab the one you just left. If a player steps off his stone, he must return to the starting line. The first to cross the finish line wins.